Ultra Mobile Broadband (UMB) combines the best aspects of CDMA, TDM, Layer Superposed (LS)-OFDM, OFDM, and OFDMA into a single air interface using sophisticated control and signaling mechanisms and advanced antenna techniques in order to deliver ultra-high fixed and mobile broadband performance.
UMB supports a forward link up to 288 Mbps and a reverse link up to 75 Mbps while mobile and an average network latency of 16.8 msec. Furthermore, voice over IP (VoIP) of more than 500 simultaneous users over 10 MHz is facilitated while mobile. Moreover, UMB will enable the convergence of IP-based voice, broadband data, multimedia, information technology, entertainment and consumer electronic services.
UMB can efficiently support OFDMA MAC/Physical and fully support centralized as well as distributed access networks. Inter-access network interfaces are streamlined and fast layer 2 handoff is supported with seamless handoff across air interface revision boundaries.
FIG. 1 illustrates a UMB centralized access network support. As illustrated in FIG. 1, each mobile station or access terminal (AT) maintains a separate protocol stack for each access network (AN) in the active set, with each protocol stack called a “route.” Furthermore each base station controller (BSC) is a separate AN.
FIG. 2 illustrates a UMB distributed access network. As illustrated in FIG. 2, each AT in this network arrangement maintains a separate protocol stack for each AN in the active set and each cell is a separate AN.
UMB simplifies the inter-AN interface by requiring each AT to support multiple routes. A simpler inter-eBS interface leads to standardized, inter-operable implementations.
Each eBS in the active set uses a separate data route and there is no need to transfer RLP and header compression states between eBSs. Traffic flowing between an eBS and an AT can be tunneled through the serving eBS, thereby supporting fast and seamless re-pointing between cells.
Signaling messages of protocols between an eBS and an AT can be tunneled through the serving eBS. No eBS has to maintain a connection state of other eBSs in the active set.
UMB layering also reduces the number of protocols in the data path. FIG. 3 illustrates UMB layers in which the application layer provides a signaling application, IP, RoHC, EAP and inter-technology tunneling. The radio link layer provides RLP and associated protocols. The MAC layer provides a packet consolidation protocol and control of physical layer channels. The physical layer defines characteristics of air interface channels. The security functions are protocols for ciphering, message integrity, and key exchange. The route control plane controls the creation and maintenance of air interface protocol stacks, one for each eBS. The session control plane provides session negotiation. The connection control plane controls the connection between the AT and an eBS.
In mobile communication systems, a base station may send to a mobile station timing adjust commands in response to an access probe. In an asynchronous mode, the base station adjusts the mobile station timing at both call set-up and hand-offs. In a synchronous mode, however, the base station is able to adjust the mobile station timing, only at call set-up.
To communicate with stationary nodes in a communication network, a timing adjust command may be transmitted to maintain alignment of OFDM symbols in the reverse link (RL) (i.e., communication from the stationary node to the base station) among all the nodes in a sector or cell. However, for mobile stations (i.e., non-stationary nodes), such alignments may not be maintained in RL OFDM due to their mobility.
Generally, a mobile station's timing is affected by twice the value of the propagation delay to account for the RL propagation delay from the mobile station back to the base station. The mobile stations in a network use the same system time, offset by the forward link (FL) (i.e., communication from the base station to the mobile station) propagation delay from the base station to the mobile station. System time is synchronous to coordinated universal time (i.e., UTC time) and uses the same time origin as global positioning system (GPS) time.
Accordingly, all base stations use the same system time within a small error tolerance. Mobile stations, in contrast, use the same system time offset by the propagation delay from the base station to the mobile station. When a mobile station is located close to a base station, as the mobile station moves towards the edge of a cell (i.e., cell-edge) and as the propagation delay increases, the mobile station timing becomes delayed relative to those of other mobile stations because the mobile station's system time is offset by the network system time due to the FL propagation delay.
For example, if a base station to cell-edge distance is 1.25 km, a propagation delay change of (2*1250 m/(3.0 e+08 m/s)) 8.3 micro-seconds may result. Such a propagation delay exceeds the cyclic prefix (CP) duration of 6.51 micro-seconds. Cyclic prefix is a repeat of the end of a symbol at the beginning of a subsequent transmission to allow multipath to settle before the main data arrives at the receiver. Unfortunately, due to multipath delays, the above-noted change in timing is typically exacerbated in networks employing fractional frequency reuse where the coverage extends beyond the cell radius into neighboring cells, and areas having great cell-site to cell-site distances. In such cases, to maintain alignment, the base station would need to be able to send a timing adjust or advance command to the mobile station.
Further, when a mobile station located at the cell-edge, as the mobile station moves towards the base station the propagation delay decreases. As a result, the mobile station timing advances relative to those of other mobile stations. In such a case, to maintain alignment, the base station would need to be able to send a timing adjust delay command to the mobile station. The current systems and communication networks do not adequately address this need.
Systems and methods are needed to overcome the above-noted problems.